FIG. 3 is a perspective view showing a prior art end surface light emission type LED. In FIG. 3, the reference numeral 1 designates an n type substrate, the numeral 2 designates an n type cladding layer as a lower cladding layer, the numeral 3 designates an active layer, the numeral 4 designates a p type cladding layer as an upper cladding layer, the numeral 5 designates an insulating film, the numeral 6 designates a p side electrode, and the numeral 7 designates an n side electrode.
When a forward direction voltage bias is applied to the end surface light emission type LED of FIG. 3, a current flows in the central portion of the element which is concentrated where the insulating film 5 is removed in a stripe configuration, and it is converted into a light in the active layer 3. The light generated in the active layer 3 is confined by the n type cladding layer 2 and the p type cladding layer 4, and is transmitted within the active layer 3 and emerges from the end surface as a light output.
In the prior art end surface light emission type LED of such a construction, there is no mechanism for confining the light in the direction parallel with the junction surface, and therefore the broadening of the output light in the horizontal direction is especially large. Even in a case where a light confinement structure is provided in the transverse direction, the end surface light emission type LED has low directionality, and the broadening of the light is large. Therefore, it is only possible to couple a portion of the output light of the LED input to an optical fiber having a small core radius, thereby resulting in a low fiber coupling coefficient.
Conventionally, there is a method in which a spherical lens is attached to the light output end surface in order to improve such a low coupling efficiency. In such a method, however, it is difficult to attach a spherical lens to the light emission region precisely because of the small sized light emission region, and to do so in mass production since a spherical lens has to be attached to each element.